The present invention relates to a rubber composition and a competition tire using the same.
Tires for motocross competition have blocks that are at least 2 cm high and in order to sufficiently exhibit a pattern effect, the hardness of the rubber must be high. Therefore, rubber compositions for motocross tires contain a small amount of process oil and a large amount of carbon black.
In the conventional composition, the gripping performance until the temperature increase of the tire due to external work is stabilized (initial grip) and the gripping performance in low temperatures are sacrificed. Particularly, on short circuits specially set up inside stadiums, performance when starting is important and improvement of initial grip is demanded.
For example, JP-A-8-333484, JP-A-11-209517, JP-A-11-209518 and JP-A-2002-332381 disclose technology for improving steering stability, rolling resistance, abrasion resistance and wet skid performance of a tire. However, such technology, which is directed to tires of passenger cars, is problematic in that the energy loss at a relatively high temperature range of 30 to 100° C., which is necessary for exhibiting the high gripping performance required in competition tires, is small, for the reason that the amount of vinyl in SBR obtained by solution polymerization is small. Consequently, the above technology does not provide satisfactory gripping performance for competition tires.
The present invention aims to provide a rubber composition, which has improved gripping performance that is required in a competition tire, high hardness and high stiffness.